Nader Runs Again, This Time With Feeling
Focus on presidential campaign of Ralph Nader, nation's foremost anti-corporate crusader who is running again as third party candidate, but on Green Party line; he insists current drive is serious, compared with 1996, when he refused to raise money, spent less than $5,000 and attracted barely 1 percent of vote; goal of current campaign is not to win, but to get more than 5 percent of vote to qualify for millions in federal campaign matching funds he says he would use to build Green Party; photo (M)